Depends on your citizenship or residency. In all cases, a valid passport is required. Switzerland is not a member of the European Union (EU).

However, Switzerland allows citizens of most "Western" countries to enter without a visa for up to 90 days.

Complete details here (choose the country that issued your passport):
http://tinyurl.com/5rkm7q



The same applies to citizens of other countries who hold valid EU or USA/Canada permanent residency credentials.

Details here (choose the country that issued your permanent residency card):
http://tinyurl.com/6xavry



Note that Switzerland is in the process of becoming a party to the Schengen agreement (which already has eliminated border controls throughout most of Western Europe). Apparently Switzerland will join Schengen around Dec 12 or 13, 2008.